A major problem in contemporary cardiology is how best to identify the patient who is at risk of dying suddenly. Techniques currently available for this purpose, such as the exposure of malignant arrhythmia by exercise testing and ambulatory monitoring, suffer major limitations. Invasive electrophysiologic techniques are now being used for the study of patients who have already suffered a major arrhythmia. One such method is the provocation of the repetitive ventricular response (RVR). The technique involves the delivery of timed premature ventricular stimuli of varying intensity, in order to elicit one or more coupled responses. It has been shown in animal studies that the ability to provoke RVR is directly related to the relative electrical stability of the myocardium measured by the myocardial vulnerability to ventricular fibrillation. Human studies have likewise shown that patients who have had a recent myocardial infarction and who manifest RVR are at an increased risk of dying suddenly. However, the frequency, reliability, reproducibility of the RVR in patients with coronary artery disease, who do not have symptomatic arrhythmia, remain to be determined. Our study will attempt to define the prevalence of the RVR in such a stable coronary population. We will also seek to define the relationship between the presence of RVR and the severity of ischemic heart disease measured angiographically and hemodynamically. In addition, we will compare the incidence of the RVR with the incidence of malignant ventricular ectopic activity exposed by prolonged ambulatory monitoring and/or exercise testing. Finally, we will endeavor to make some statement regarding the reproducibility of the technique by studying patients, whose symptoms and medications are constant, at two widely separate points in time. The ability to identify patients with ischemic heart disease who may die from a malignant arrhythmia would be an important breakthrough in cardiology practice. We hope to contribute to the solution of this important problem by defining the utility of an electrophysiological technique, the provocation of the repetitive ventricular response.